CHAPEL HILL -- Two studies reported in Thursday's (July 20) New England Journal of Medicine support what many doctors already believed -- that colon cancer screening known as sigmoidoscopy fails to detect a substantial proportion of symptom-free cancers and polyps that may turn cancerous.
The research, conducted at Indiana University, the University of North Carolina at Chapel Hill and various U.S. Veterans Affairs medical centers, suggests that many lives might be saved if colonoscopy screening were done every five to 10 years for people over age 50.
Dr. David F. Ransohoff, professor of medicine at the UNC-CH School of Medicine, helped design, analyze and write one of the studies led by his former trainee Dr. Thomas F. Imperiale, now at Indiana University. That work involved 1,994 consecutive colonoscopies among apparently healthy employees of Eli Lilly in Indianapolis, which paid for the screening.
The goal was to determine the risk of cancer or possibly precancerous growths high in the colons of adults depending on whether they had small growths known as polyps closer to their rectums.
"We wanted to learn whether what's found with sigmoidoscopy can predict lesions that could be identified only with colonoscopy," said Ransohoff, a member of the UNC Lineberger Comprehensive Cancer Center. "The short answer is no, but that doesn't surprise us."
Both procedures involve physicians inserting lighted tubes into the rectum to check the colon wall for cancer and other abnormalities. In sigmoidoscopy, the flexible, telescope-like tube is shorter and can show only about a foot-and-a-half of the colon. With colonoscopy, the device can show all three to five feet of the lower intestine but it takes longer, costs more, is slightly riskier and requires both a specialist and sedation.
The Indiana and North Carolina researchers found that asymptomatic people who had polyps in the lower colon were more likely than those who did not to have cancer and other precancerous growths higher up, Ransohoff said. However, if colonoscopy is performed only on people with polyps near the rectum, half the cases of cancer and other growth higher up will be missed.
Led by Dr. David A. Lieberman of Portland Veterans Affairs Medical Center, the second study of 3,121 veterans at 13 U.S. centers showed comparable results. Ransohoff called the two projects important because of their large size and because they were studies of screening colonoscopy involving patients without symptoms.
"The barrier to reducing the number of deaths from colorectal cancer is not a lack of scientific data but a lack of organizational, financial and societal commitment," wrote Dr. Daniel K. Podolsky in an accompanying editorial. "All persons 50 years of age or older who are at average risk for colorectal cancer should undergo comprehensive evaluation of the entire large bowel."
Podolsky, a Massachusetts General Hospital physician, said he believed such screening was best accomplished by colonoscopy rather than by barium-enema evaluations given the results of recent comparative studies. Regardless, either form is superior to sigmoidoscopy or no screening.
"If a patient has no abnormalities, colonoscopy need not be repeated for at least five years and perhaps up to 10 years," he wrote. "As many people have pointed out, relying on flexible sigmoidoscopy is as clinically logical as performing mammography of one breast to screen women for breast cancer. It is time to go the distance."
Ransohoff agreed that colorectal screening for cancer is an important national issue, but said that the two new studies address only one of several issues policy-makers must consider before making firm recommendations.
"You have to make decisions about screening colonoscopy based on safety and cost and the additional benefit of colonoscopy compared with other strategies," he said. "These two studies address only one small piece of the puzzle. Further, they confirm what policy-makers already believed about the lack of thoroughness of sigmoidoscopy. The two studies cannot by themselves be used to answer the larger policy question of whether screening colonoscopy should routinely recommended for everybody over age 50."
More than 47,000 Americans die from colon cancer each year, and another 8,600 die from rectal cancer. Most of those deaths could be prevented if the tumors were caught earlier, doctors agree. Colorectal cancers are the third most common cancers in men and women, and an estimated 130,200 new U.S. cases will occur this year.
July 19, 2000 -- No. 373
By DAVID WILLIAMSON UNC-CH News Services
Note: Ransohoff can be reached at 919-966-1256.
Journal
New England Journal of Medicine